1. Technical Field
The present invention relates in general to disk drives and, in particular, to an improved system and apparatus for vibration damping of integrated lead suspensions in high density magnetic storage devices.
2. Description of the Related Art
Data access and storage systems generally comprise one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device (DASD) or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic coating. Typically, one to five disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm).
A typical HDD uses an actuator assembly to move magnetic read/write heads to the desired location on the rotating disk so as to write information to or read data from that location. Within most HDDs, the magnetic read/write head is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is aerodynamically shaped to glide over moving air in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk.
A slider is typically formed with an aerodynamic pattern of protrusions on its air bearing surface (ABS) that enables the slider to fly at a constant height close to the disk during operation of the disk drive. A slider is associated with one side of each disk and flies just over the disk's surface. Each slider is mounted on a suspension to form a head gimbal assembly (HGA). The HGA is then attached to a semi-rigid actuator arm that supports the entire head flying unit. Several semi-rigid arms may be combined to form a single movable unit having either a linear bearing or a rotary pivotal bearing system.
The head and arm assembly is linearly or pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk. When current is fed to the motor, the VCM develops force or torque that is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head approaches a desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop and settle directly over the desired track.
With increasing data densities, off-track motion related to integrated lead suspension (ILS) vibration has become a significant contributor to track misregistration (TMR). Airflow from the disks is the primary excitation mechanism for the ILS and the resulting ILS vibration introduces off-track to the head by deflecting the HGA. Previous solutions for minimizing ILS vibration include guide slots formed in the actuator arm and drops of adhesive that secure the ILS to the actuator arm at multiple locations.
In FIG. 1, for example, the rotary actuator 11 of a disk drive is subject to airflow-induced vibration that adversely affects performance. In a typical design, the conductive traces on the ILS tail 13 that extend from the HGA 15 are soldered to the pads 17 on a flexible cable assembly 19. In such an arrangement, airflow from the rotating disks impinges on the ILS traces and the resulting trace vibration produces an off-track motion of the head that the disk drive perceives as TMR. The orientation of the actuator within the rotating disk pack has a significant impact on how the airflow excites the ILS traces. For instance, when the head is at the OD of the disk, the airflow excitation driving ILS vibration has axial as well as radial and tangential components. However, when the head is at the ID of the disk, ILS vibration is primarily driven by in-plane airflow. As there are multiple resonant frequencies of the ILS trace and the nature of the airflow excitation changes as a function of actuator orientation, a robust solution that addresses this problem would be desirable. What is proposed in this disclosure is the addition of a constrained layer damper (CLD) on the ILS that also minimizes the extent to which the ILS will vibrate.